Field of the Invention
The present invention relates to a stereo boundary microphone using, for example, two unidirectional microphones and a stereo boundary microphone adapter.
Description of the Related Art
A boundary microphone (on-surface sound pickup microphone) is usually used in a conference room or a broadcast studio.
When used in a conference room, the boundary microphone is placed on a table. When used in a broadcast studio, the boundary microphone is placed on a table or on a floor so as not to be apparent (not to be shot by a television camera).
As disclosed, for example, in JP H8-65786 A and JP 2013-527995 W, the boundary microphone is configured with a boundary plate and a microphone held on the boundary plate.
The microphone is placed close to the boundary plate. The direct sound and the reflected sound from the boundary plate entering the microphone have almost no time-gap (phase difference). Accordingly a clear high acoustic signal can be collected by the boundary microphone.
For stereo sound collection technique using two unidirectional microphones, A-B technique and X-Y technique are known. In the A-B technique, microphones are positioned with a relatively large distance therebetween to create stereo effect by a time-gap. In the X-Y technique, microphones are positioned so as their sound collection axes intersect by a certain angle (for example, 90 to 120 degrees) to create stereo effect by the difference in level of sounds entering the two microphones.
A stereo boundary microphone employing stereo sound collection technique, such as the A-B technique and the X-Y technique, is disclosed in JP 2002-300683.
FIG. 13 illustrates an example stereo boundary microphone employing the X-Y technique.
As illustrated in FIG. 13, two unidirectional microphones 5L and 5R are held on a boundary plate 11 having a rectangular shape. In this example, the two unidirectional microphones 5L and 5R are positioned so as sound collection axes LX and RX of the microphones 5L and 5R, respectively, to be parallel with the top face of the boundary plate 1 and intersect with each other at 120 degrees.
In this configuration, difference in level of sounds entering the two microphones 5L and 5R is produced, and this difference creates stereo effect. With the effect of the boundary plate 11 positioned to be parallel with the sound collection axes LX and RX, the microphones 5L and 5R receive clear acoustic signals for left and right channels.
The stereo boundary microphone illustrated in FIG. 13 has left and right unidirectional microphones 5L and 5R positioned so as to face each other at a predetermined angle above the boundary plate 11. In such a configuration, a large positioning region (area) is necessary for two microphones.
Moreover, audio output cords 6L and 6R of microphones are routed out through both sides of the boundary plate 11. For this reason, conventional boundary microphones disadvantageously have messy and unfavorable external appearance and difficulty in downsizing.